It is known that an aromatic polyimide resin article shows very favorable physical and chemical characteristics such as high mechanical strength, high heat resistance, and high resistance to chemical compounds. Accordingly, the aromatic polyimide resin has been widely employed for manufacturing substrate plates of electronic devices. The favorable physical and chemical characteristics of the aromatic polyimide resin have recently received increased attention, and hence the aromatic polyimide resin has been studied for the use in manufacturing various constitutional units of aeroplane and spacecraft. In fact, some aromatic polyimide resin articles are employed in these technical fields.
An aromatic polyimide article such as an aromatic polyimide sheet is generally manufactured by first preparing a solution of a polyamic acid (i.e., polyamide acid) by the reaction between an aromatic tetracarboxylic acid derivative and an aromatic diamine in a solvent, spreading the polyamic acid solution on a temporary support to prepare a polyamic acid sheet, and finally heating the polyamic acid sheet to give the polyimide sheet upon drying and cyclization reaction.
An aromatic polyimide article having a large thickness or an aromatic polyimide article of non-sheet form is generally manufactured utilizing a plurality of prepregs. A plurality of the prepregs are laminated one on another and then heated under pressure to give an aromatic polyimide article. The prepreg is prepared by impregnating a sheet matrix of a reinforcing fiber with a thermosetting polymer solution composition.
Japanese PCT publication 2002-511902 discloses a method of preparing a prepreg from a polyimide precursor solution which has a solid concentration of 50 to 80 wt. %, a volatile concentration of not higher than 35 wt. %, and a Brookfield viscosity of 4,000 to 10,000 cP. The typical polyimide precursor solution is prepared from oxydiphthalic dianhydride, phthalic acid and 3,4′-oxydianiline. The solvent of the solution typically is a mixture of N-methyl-2-pyrrolidone and ethanol.
Japanese Provisional Patent Publication 2000-219741 A describes a terminal modified imide oligomer solution (thermosetting solution composition) which is obtained by the reaction of 2,3,3′,4′-biphenyltetracarboxylic acid with an aromatic diamine compound and 4-(2-phenylethynyl)phthalic anhydride and further describes that the solution composition is employable for manufacturing a prepreg and further an aromatic polyimide article (i.e., cured article). The publication describes a list of solvents employable for the preparation of the solution composition which includes N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N-caprolactam.
Japanese Provisional Patent Publication 2004-331801 A describes that 2,2′,3,3′-biphenyltetracarboxylic dianhydride is employable for the preparation of an aromatic polyimide as the aromatic tetracarboxylic acid compound, and further describes that the dianhydride is reacted with an aromatic diamine compound in the presence of a reactive crosslinking agent to give a polyamic acid oligomer.
The thermosetting solution composition comprising the terminal modified imide oligomer solution prepared by the reaction of 2,3,3′,4′-biphenyltetracarboxylic acid with an aromatic diamine compound and 4-(2-phenylethynyl)phthalic anhydride in a solvent is of value for preparing an aromatic polyimide article (i.e., cured article) having excellent physical and chemical properties. However, all solvents described in the publication as the solvents employable for the preparation of the imide, that is, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N-caprolactam, have a high boiling point. Therefore, removal of the solvent from the solution composition by evaporation requires high temperatures and long periods of time. These evaporation conditions are not favorable from the viewpoint of industrial preparation.